System and method for undersea micropile deployment

ABSTRACT

A system for deploying an undersea anchor is provided, where the system includes a controller programmed and configured to monitor the drilling and grouting of micropiles in real-time and compare the metrics detected by such monitoring against pre-determined design criteria to substantially ensure micropile deployment meets the design criteria upon completion of the drilling and grouting process during micropile deployment. The system may also include means for pre-tensioning the micropiles after deployment, where the controller is programmed and configured to determine whether the pre-tensioning process conforms to design criteria.

RELATED PATENT APPLICATIONS

The present application claims priority from provisional applicationSer. Nos. 61/736,477 filed on Dec. 12, 2012, and 61/755,401 filed onJan. 22, 2013, both of which are incorporated herein in their entiretyby reference.

BACKGROUND

The present invention relates to the drilling, monitoring, placement andpre-tensioning of micropiles configured for use and deployment in anundersea environment.

In that regard, micropiles have been employed historically to withstandcompressive and tensile loads in terrestial contexts. Where it isdesired to secure an anchor to a seafloor bed, conventional approachesto appropriate design and proper application of an anchor or foundationsystem on a seafloor site are often based on expensive and timeconsuming geotechnical survey and analyses of survey results of theseafloor on which the anchor or foundation will be installed.

Also, without pre-stressing, a conventional marine micropile anchorinstalled on a seafloor, lake bed or river bed may be subjected tofatigue, corrosion, cracking, uplift and an inability to deal withlateral loading. Other conventional anchor systems used in a marineenvironment do not incorporate pre-stressed elements and thus may besubject to these same problems. The present systems and methodologiesprovide beneficial improvements to the prior art systems.

SUMMARY

A significant portion of the geotechnical survey effort required forconventional approaches to planning seafloor anchors can be eliminatedby measuring seabed properties in real-time, in-situ as part of theanchoring or foundation system micropile installation process. Thesystem and method of the present application differs from what currentlyexists. During micropile anchor installation as described herein,seafloor properties may be measured and adjusted for in real-time duringthe drilling process, eliminating the need for geotechnical surveys inadvance of the installation. A considerable amount of time and expenseis required for current micropile anchor planning and installation andthis time and expense may be reduced dramatically or eliminated with thesystem and method of the present disclosure. Further, the real-timemeasurement of seafloor properties during installation of anchorsensures the best anchor performance at a fraction of the time andexpense.

A typical candidate anchoring site may have relatively homogeneous rockor other competent material covered with a sand/mud overburden ofmoderate thickness. In these cases, the holding capacity of a micropilemay vary linearly with the embedment depth in the rock. Measureddrilling parameters such as torque, push and rate of advance may be usedto determine the transition point between sediment and rock. Therefore,the required drilling depth can be determined very accurately tomaximize installation efficiency. Similarly, in the case where theoverburden is extensive, additional micropile lengths can be installedso the full required embedment depth into competent material is met.

In addition, the drilling rate of advance in rock or any other materialcan be measured for a given set of conditions and yield informationregarding seabed strength. Significant variations in the strength of theseabed could be identified during drilling and adjustments to theoperations such as varying the total micropile embedment length toobtain the required holding capacity could be made.Measure-while-drilling modeling and simulation software will allow forinstallation planning that only depends on general seafloor parameters,not on detailed geotechnical survey results. Various seafloor parametersfor modeling and simulation may dictate corresponding actions formicropile anchor installation planning. Sensor input to themeasure-while-drilling software will determine the correspondingreal-time control during drilling to install the micropile anchor.

A possible exemplary process for making the system of the presentdisclosure may be as follows: measure-while-drilling modeling andsimulation software may be coded in cooperation with subject matterexperts specifying the logic for the program. The suite of down-holesensors may be selected to provide input to the real-time monitoringsoftware that would be coded to effect adjustments to the drillingcontrol accordingly. The modeling and simulation planning software wouldbe optional to the real-time drilling sensors and monitoring software.It is not intended or required that the planning software must beintegrated with the real time monitoring software but it is anticipatedthat such integration may be possible within the scope of the presentdisclosure.

The system of the present disclosure may be further operated in thefollowing exemplary fashion: measure-while-drilling modeling andsimulation software may allow for drilled and grouted seafloor micropileanchor installation planning. Micropile anchor installation may becontrolled by the use of sensors placed within the hole being drilledand/or on the drill itself that measure real-time parameters of thedrilling progress and the calculated drilling adjustments required todetermine the required anchor holding capacity. Once installed,micropile strength also can be confirmed or verified as part of theinstallation process.

Pre-stressing the micropiles used to secure a sea anchor or marinemooring to the bed of a body of water may help to limit or restrictstructural movement of the anchor due to anchor micropile elongationcaused by cyclic and dynamic loads. Micropiles used for such anchors aretypically made of steel that are driven into a position within the bedto provide resistance to movement of the anchor. When the anchor issubjected to forces being placed on the anchor by an object or structurethat is connected to the anchor, these forces are transmitted to themicropiles, which can deform the micropiles or possibly shift them. Thismay compromise the integrity of the anchor, making it more likely tofail, or may permit an undesirable movement or displacement of theobject or structure secured to the anchor.

In the context of the present application, pre-stressing means theintentional creation of permanent stresses in a structure for thepurpose of improving the structure's performance under various serviceconditions. For marine applications of micropiles, it is desirable thateach micropile in an anchor or other bottom fixing assembly be loadtested to verify its capacity and that load be “locked in” to maintain apre-stress to counteract the stresses resulting from the appliedvertical and/or lateral mooring load to the assembly. Pre-stressing willhelp limit or restrict structural movement caused by cyclic and dynamicloads. Micropile pre-stressing for the purpose of achieving an anchorsystem capable of resisting vertical and lateral mooring loads isinnovative and un-proven in the sub-sea environment; however, it isvital if micropiles are to be used efficiently for mooring systems.

Pre-stressing may provide the following benefits for a marine groutedmicropile anchor system:

-   -   Proof test. Each micropile may be pre-stressed to ensure that it        will hold its design load in accordance with industry standards.    -   Maintain axial compressive force. Pre-stress creates an axial        compressive load in each grouted micropile, which in turn        generates a lateral frictional resistance by means of the        interaction between a template frame or micropile head and the        seabed soil.    -   Eliminate uplift. Pre-stress will help avoid unequal load        distribution in a micropile system. It counteracts uplift and        overturning loads caused by environmental loads from wind, waves        and current.    -   Eliminate fatigue. Fatigue failure is minimized since the        effects of cyclic loading that causes fatigue failure may be        reduced or eliminated.    -   Eliminate cracking. Pre-stress precludes grout cracking Long        term, progressive grout failure could result in total loss of an        anchorage.    -   Corrosion protection. Any micropile elongation will        progressively break down and crack the protective grout cover,        possibly leading to corrosion and failure of the micropile.        Pre-stress eliminates micropile elongation through the grout        column thus maintaining the corrosion protecting grout cover.

The system and method of the present disclosure differs from whatcurrently exists. This system and method represent a new capability formicropiles or micropiles used in a marine environment.

A conventional non-pre-stressed system can allow movement of individualmicropiles, which will lead to premature failure of the anchor and alsowill not help the anchor deal with any loads other than pure tensionloads. The dynamic forces exerted on objects and structures secured toanchors in a marine environment are likely if not certain to place loadsother than pure tension loads on the anchors to which they may besecured. Pre-stressing each individual micropile used as part of a seaanchor and locking that stress or load into each individual micropilewill help maintain the compressive stress in each micropile and willserve to limit or restrict structural movement of the micropile andtherefore the anchor.

The system and method of the present disclosure may incorporate thefollowing elements, even though it is not intended to limit the scope ofthe present disclosure to just this set of exemplary elements:connecting a jacking or pre-stressing system to an anchor micropile;remotely operating the jacking system; applying a tension load to themicropile in increments with the jacking system while measuring the loadand any elongation of the micropile; upon reaching a specified load orloading condition, lock load at that level; and disconnecting thejacking system from the micropile after locking the load and applying asimilar process to any remaining unstressed micropiles.

The pre-tensioning device is attached to micropile. The pre-tension loadis applied to the micropile. The pre-tensioned micropile is locked witha locking device. The system is moved to the next micropile. Aspre-tension is applied, the micropile elongation and load will bemeasured using remote system controller until desired load is reached.

The most common and accurate way to pre-stress an anchor is direct pull,which may use a hydraulic jack that connects directly either at theanchor head or at a pulling head attached to the pre-stressing steel.Hydraulic jacks capable of developing 100 percent of the specifiedminimum tensile strength (SMTS) of available micropiles are availableand can be adapted for sub-sea use. The jack frame typically bearsagainst a steel plate while the hydraulic jack transfers a directtension load to the anchor. When the pre-stress load is reached, a nutor other locking device may be turned against the anchor bearing plate,and the load from the jack may be released. The locking device or nutprevents the steel from relaxing back to its original length to maintainthe pre-tension. Additional elongation in the anchor rod only occurs ifthe applied load exceeds the pre-stress load. The pre-stress load istypically 133% to 150% of the design load to allow for minor loadrelaxation, which may typically occur once the jack load is released.

A pressure gauge and dial gauge are used for terrestrial applications,but sub-sea pre-stressing may require a marinized load cell and a lineardisplacement transducer if the jacking device is to be controlledremotely. A remotely operated micropile pre-stressing system accordingto the present disclosure for use in a sub-sea setting may include thedirect pull apparatus or jacking device, a load lock-off system,load-displacement measurement system and the mechanism and controllerrequired to pre-stress multiple micropiles on a single template oranchor.

It is anticipated that commercially available conventional componentsmay be marinized and integrated into the system of the presentdisclosure. A remote control and underwater operation capability willneed to be developed for these conventional components to permit thesystem and method of the present disclosure to operate as describedherein. Algorithms to account for different depths of water where thesea anchors may be positioned will need to be developed to ensure thatthe load measured accurately reflect the load that a micropile is beingsubjected to.

Thus, in one embodiment, a system is provided for more effectivelydeploying an undersea anchor, where the system comprises a controllerprogrammed and configured to monitor the drilling and grouting ofmicropiles in real-time and compare the metrics detected by suchmonitoring against pre-determined design criteria to substantiallyensure micropile deployment meets the design criteria upon completion ofthe drilling and grouting process during micropile deployment. In someembodiments, the system further comprises means for pre-tensioning themicropiles after deployment, where the controller is programmed andconfigured to determine whether the pre-tensioning process conforms todesign criteria.

BRIEF DESCRIPTION OF THE FIGURES

The aforementioned objects and advantages of the present invention, aswell as additional objects and advantages thereof, will be more fullyunderstood hereinafter as a result of a detailed description of apreferred embodiment when taken in conjunction with the followingdrawings in which:

FIG. 1 shows a perspective schematic view of one embodiment of thepresent invention;

FIG. 2 shows an elevational schematic view of the embodiment of FIG. 1;

FIG. 3 shows a flow chart reflecting one methodology of the presentinvention;

FIG. 4 shows a perspective schematic view of an alternative embodimentof the present invention.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

By way of example, and referring to FIGS. 1 and 2, one embodiment of thepresent system comprises an anchor system 10 suitable and configured foruse in securing a buoyant load from a sea floor, whether or not the seafloor is generally horizontal, slightly sloped, or significantly sloped.In that regard, one example of anchor system 10 comprises an anchorplate 12 that may comprise a frame of generally planar configuration,but may be structured and/or reinforced in one of numerous possiblearrangements. In the example shown in FIG. 1, the anchor plate comprisesbearing plates 14 for securing a plurality of micropiles 16 at relativeangles to each other; i.e., one set directed at a first angle, and asecond set at a second angle. Even within each set, the angle ofdeployment of the micropiles 16 may be different relative to each other.The bearing plates 14 serve to permit the deployment and post-tensioningof the micropiles, as discussed below. The anchor plate furthercomprises one or more anchor points 18 from which the buoyant load maybe secured. In this example, the anchor points 18 comprise cableshackles or eyes to which a cable may be secured to tie-down whateverload bearing device is desired, including a buoy, an oil rig, amonument, etc.

The micropiles are secured to the bearing plate mechanically via a nutand washer arrangement 20, although other mechanical means may beemployed. Each micropile is contemplated to comprise a length ofthreaded rod 22, one or more couplings 24 to join the rods 22 togetherto extend the length of the micropile as needed for depth of deployment,and a drill bit 26 at the distal tip of the micropile for creating thebore into which the micropile is deployed. Referring to FIG. 2, it canbe appreciated that a drill 28 can be employed to bear against thebearing plates 16 to drill the micropile in rod sections 22, joiningthem together using the couplings 24. Such a drill 28 can be remotelycontrolled and powered through cable 30. In that regard, any micropiledrill may be employed.

In the example shown in FIGS. 1 and 2, the anchor system 10 has beendeployed pursuant to design criteria based upon a pre-existinggeophysical and soil condition survey to assess the ability of theanchor location to bear the desired load. Referring to FIG. 3, oneexample of an inventive methodology can be described. It is contemplatedthat a measure-while-drilling technique be employed to more effectivelydeploy an anchor system, such as that shown in FIGS. 1 and 2, as well asFIG. 4 described below. The advantages of such a technique are addressedabove. It is also contemplated that a pre-tensioning technique beemployed as well for effective anchor system deployment, the advantagesof which are also addressed above. The invention described herein mayemploy one or both of the techniques as desired, but will be describedas being used together for purposes of simplicity. It should be notedthat as part of the micropile deployment, it is typical for a thin groutto be delivered while the drill is being drilled, and then followingcompletion of the drilling process, when the micropile is fullydeployed, a rich grout is delivered to surround the micropile and createa grout/soil interface with sufficient friction to resist the desiredload upon the anchor system.

With reference to FIG. 3, an anchor deployment system comprises a drill,a grout system, a tensioning and instrumentation system, a data feedbacksystem, and a controller. Such an arrangement is by example only. Inthis example, the drill is configured to be controlled pursuant tocertain metrics, as is the grout system, so that certain metrics aremeasured in real-time during the drilling and grouting process andmeasured against the desired design criteria to better ensure that theresulting deployed micropiles and anchor system are compliant with thedesign criteria. In that regard, in one embodiment, certain drillingsensors are monitored, including torque, rate of advance, applied force,and rotational speed, which can be measured using, for example, ahydraulic pressure sensor, a linear sensor, a load cell, and a rotationsensor, respectively. Likewise, during delivery of first the thin groutand then the rich grout, both flow and pressure are monitored using aflow meter and a pressure transducer, respectively. In the case of therich grout, density may also be monitored using a densimeter if sodesired. During the drilling and grouting process, feedback from thevarious sensors are provided to the feedback system (i.e., DataAcquisition System), and fed to the controller for purposes of employingsoftware that compares the progress of the deployment with the desireddesign criteria. This permits adjustments to be made in both thedrilling and grout delivery metrics to accommodate any deficienciesencountered. Once the micropile has been appropriately deployed, alongwith the rich grout, with time for the grout to set, the system can thenactuate the tensioning system by applying a pile-tensioning mechanism toload the micropile in tension before tightening the micropile againstthe bearing plate or the anchor plate, depending upon whether a bearingplate is used. The pre-tensioning system would be controlled andcompared against a micropile performance model loaded into thecontroller for purposes of knowing when to stop the pre-tensioning step.Once completed, the result is a micropile that meets the desired designcriteria. Following such procedure with the balance of the suite ofmicropiles permits an effective deployment of an anchor systemsufficient to meet the load requirements desired. If so desired,multiple drills 28 may be employed simultaneously to speed up theprocess where there are a large number of piles being deployed. The samemay be true for the pre-tensioning mechanism.

Referring to FIG. 4, another example of an anchor system 110 can beappreciated. As described above, the anchor plate 112 may be one of anynumber of possible configurations, such as that shown in FIG. 4, wherethe micropiles 116 are arranged radially rather than in a grid pattern.In the example shown, the micropiles 116 are also deployed normal to theanchor plate 112. In this particular example, a multi-pile drillingsystem 128 is employed, where at least two micropiles 116 are beingdrilled and deployed simultaneously, each individually controlled by thecontroller based upon the metrics detected in the feedback loop. Thedrill 128 can then be removed upon complete deployment of themicropiles, leaving the anchor plate 112 in place.

It is contemplated that the systems and methods of the present inventionmay be applied to terrestrial micropile and anchor construction. Theremay be land-based micropile and anchor construction locations that donot permit the control and operation systems to be positioned at theanchor site. The systems of the present invention may permit the controlof the jacking system to be handled remotely, whether the anchorlocation is underwater or in a difficult location above water. It isanticipated that embodiments of the present invention may preferablyhave a robust testing and calibration capability to ensure thatmicropiles are subjected to accurately measured loads.

Persons of ordinary skill in the art may appreciate that numerous designconfigurations may be possible to enjoy the functional benefits of theinventive systems. Thus, given the wide variety of configurations andarrangements of embodiments of the present invention the scope of theinvention is reflected by the breadth of the claims below rather thannarrowed by the embodiments described above.

What is claimed is:
 1. A system for more effectively deploying anundersea anchor, the system comprising a controller programmed andconfigured to monitor the drilling and grouting of micropiles inreal-time and compare the metrics detected by such monitoring againstpre-determined design criteria to substantially ensure micropiledeployment meets the design criteria upon completion of the drilling andgrouting process during micropile deployment.
 2. The system of claim 1,further comprising a means for pre-tensioning the micropiles afterdeployment, where the controller is programmed and configured todetermine whether the pre-tensioning process conforms to designcriteria.
 3. The system of claim 1, further comprising drilling meansfor deploying the micropile into a seabed floor, and a grouting systemfor delivering thin grout during the drilling process and rich groutfollowing micropile deployment.
 4. A method for more effectivelydeploying an undersea anchor, the method comprising employing acontroller to monitor the drilling and grouting of micropiles inreal-time and compare the metrics detected by such monitoring againstpre-determined design criteria to substantially ensure micropiledeployment meets the design criteria upon completion of the drilling andgrouting process during micropile deployment.
 5. The method of claim 4,wherein monitoring comprises detecting the torque applied, the linearadvancement, the load and the rotation of the micropile duringdeployment.
 6. The method of claim 5, wherein monitoring comprisesdetecting the flow rate and pressure of the grout during delivery.